Field of the Invention
The present invention relates to an exhaust gas purifying device, and more particularly, it relates to an exhaust gas purifying device which is capable of efficiently removing particulates in an exhaust gas emitted from a direct injection type gasoline engine and efficiently purifying the exhaust gas.
Description of the Related Art
In recent years, to meet activation of environmental protection movement and various requirements for resource saving, energy saving and the like, there has been advanced the development of an engine which is excellent in fuel economy performance and enables long-distance and long-time running in a state where consumption of fuel such as gasoline is decreased and an amount of an exhaust gas to be emitted is decreased. Especially in a gasoline engine which is frequently used as a driving source of a car, to satisfy a request for the above-mentioned decrease of the fuel consumption, there has been advanced development of a technology concerned with a direct injection type gasoline engine which is driven by directly injecting the fuel into a cylinder.
In a conventional usual gasoline engine, differently from the above “direct injection type”, “a suction port fuel injection type” is mainly employed. In the gasoline engine in which this suction port fuel injection type is employed, it is possible to suppress an amount of a particulate matter (PM) such as soot to be generated, and influences of the particulate matter on atmospheric pollution or natural environment are not especially large. However, there has been the problem that this gasoline engine is poor in fuel economy performance as compared with the direct injection type gasoline engine.
On the other hand, in the direct injection type gasoline engine, the decrease of the fuel consumption can be promoted as compared with the usual gasoline engine. However, the amount of the particulate matter to be generated is excessively larger than before, and it is necessary to emit the exhaust gas including the generated particulate matter to atmospheric air through an appropriate treatment. That is, the treatment of the particulate matter becomes complicated, and a device or equipment concerned with the treatment is required.
On the other hand, in a diesel engine to be mounted in a large truck or the like, a trapping filter (an exhaust gas purifying device) in which a honeycomb structure is used is attached to the diesel engine for the purpose of removing a particulate matter in an exhaust gas which is generated by an operation of the diesel engine. As the honeycomb structure for use in the exhaust gas purifying device, there is mainly used a plugged honeycomb structure (see Patent Document 1) including plugging portions with which both ends are plugged in accordance with a predetermined arrangement standard. In consequence, the exhaust gas emitted from the diesel engine flows into the above plugged honeycomb structure, and passes through partition walls of the plugged honeycomb structure which are made of a porous ceramic material, whereby the particulate matter is trapped by the partition walls and deposited thereon.
As a result, the particulate matter in the exhaust gas emitted from the diesel engine can be removed by the trapping filter, and the gas passed through the trapping filter can be converted to a purified gas. However, fuel for use in the diesel engine is different from that in the gasoline engine, and hence even when the above trapping filter for the diesel engine is used as it is in the gasoline engine, the particulate matter cannot efficiently be removed.
To eliminate such a problem, the present applicant has already suggested the development of an exhaust gas purifying device which is capable of efficiently removing a particulate matter included in an exhaust gas of a direct injection type gasoline engine and is especially capable of exerting a high purifying performance even immediately after the start of the engine without increasing a pressure loss when treating the exhaust gas (see Patent Document 2).
[Patent Document 1] JP-A-2003-254034
[Patent Document 2] JP5584487